1. Field of the Invention
The present invention relates to powered handpieces for use in endophthalmic surgery.
2. Description of the Prior Art
Endophthalmic surgery, or surgery on an intact and normally pressurized eye, represents an important and relatively recent development in the field of ophthalmology. In this technique, the existing optical pathways of the pressurized ocular globe are utilized for visualization during delicate intraocular manipulations. Maintenance of positive intraocular pressure, moreover, tends to preserve and stabilize the spatial relationships among the various intraocular tissues.
The archetypal endophthalmic procedure is the cataract aspiration technique of extracapsular cataract surgery described by Scheie, Am. J. Ophthal. 50:1048 (1960), wherein an instrument is passed through a small incision at the margin of the cornea into the anterior aqueous chamber of the eye to incise the anterior capsular membrane of the lens. The aqueous, which leaks out during this manipulation, is replaced by a gravity-fed infusion of physiologic saline through a cannula inserted into the anterior chamber through a second small incision. A blunt needle is then inserted through the first incision into the lens, whereupon gentle suction aspirates the soft lens substance leaving the posterior capuslar membrane in place. Whatever volume is removed or leaks from the two small incisions is replaced by the continuous gravity feed of saline. Absent any seepage or applied suction, the pressure in the eye stabilizes at a point determined by the physical elevation of the saline column above the level of the eye. At the end of the procedure, all tubes are withdrawn and the incisions are sutured.
Conceptually, all modern endophthalmic procedures are variations and refinements of the foregoing technique. In vitrectomy, for example, an incision is made through the scleral coat of the eye between the iris and the anteromost retina. A tract is cut with a long, sharp knife into the vitreous, and the tip of the vitrectomy instrument is placed in the eye. Infusion is provided through a separate incision or through cannula concentric with the vitrectomy instrument itself. Gentle aspiration provided through the tip of the vitrectomy instrument engages vitreous or other intraocular tissues, which are then sheared or sliced in small bits and removed from the eye through an aspiration tube. Illumination is provided by optical fibers which may be concentric with the vitrectomy instrument or inserted separately. The procedure is visualized with a high magnification operating microscope. Actuation of the various functions at the instrument tip is usually by remote foot control.
The earliest powered vitrectomy instruments utilized rotary cutting elements. See, e.g., Machemer et al., Trans. Am. Acad. Ophthal. Otolaryng. 75:813 (1971). Rotary instruments, however, tended to introduce undesirable pulling or shearing to the tissue being severed. Efforts to avoid these effects led to the development of linearly reciprocating cutting instruments, an early sample of which is described by Peyman and Dodich, Arch. Ophthal. 86:548 (1971). The instrument portion of the handpiece consists of two concentric tubes with a hole near the distal end of the outer tube. Cutting is performed by the chopping action of the sharpened end of the inner tube against the plane interior end of the outer tube. Suction applied to the inner tube urges the tissue to be severed into the hole in the outer tube and then removes the severed bits of tissue from the eye. Infusion is provided through a small tube running parallel to the outer concentric tube. The necessary powered reciprocation of the inner tube relative to the fixed outer tube is provided by a small electrical solenoid, the oscillation rate of which can be varied. A description of this handpiece can also be found in U.S. Pat. No. 3,776,238, to Peyman et al.
Although electrical solenoid devices provide a readily adjustable source of linear reciprocating motion, they also possess numerous drawbacks which limit their utility in a surgical environment. They tend to be relatively heavy, for example, which renders the handpiece somewhat inconvenient to manipulate. During sustained operation, solenoid devices also tend to generate significant amounts of heat which must be isolated from delicate tissues. Moreover, since the solenoid is an integral part of the handpiece and must be supplied with an electrical current, a potential electrical hazard is presented.
Pneumatic power sources possess none of the foregoing disadvantages. Pneumatic devices are readily adaptable to linear reciprocating operation, do not inherently generate heat, and can be constructed from lightweight materials. To the extent that electrical controls are necessary, they can be confined to a pneumatic power supply unit that is connected to the handpiece by a nonconducting pneumatic supply line and is thus well isolated from the surgical site. Pneumatic devices, moreover, tend to produce a more evenly modulated power pulse than is obtainable from electrical solenoid devices. These factors render pneumatic devices well suited as power sources for powered vitrectomy instruments, and a number of pneumatically operated handpieces have been developed for ophthalmic use.
With the continual refinement of endophthalmic surgical techniques and the proliferation of specialized reciprocating instruments based on the previously-described prototype of Peyman and Dodich, there has arisen a need for a pneumatic handpiece which is compact for convenient manipulation during delicate surgical procedures, simple in construction, safe to operate in a surgical environment, and versatile in the sense of accommodating a number of different endophthalmic instruments in an interchangeable manner. Prior art pneumatic handpieces invariably fall short in one or more of these respects.
One known type of pneumatic handpiece is described in U.S. Pat. Nos. 3,815,604 and 3,884,237, both to O'Malley et al. The disclosed handpiece consists generally of a cylindrical housing, an end cap for receiving one end of a projecting sharp-edged stainless steel tube, and a piston which is slidably received within the housing for providing reciprocating motion to a second stainless steel tube coaxially arranged within the first. Near its distal end, the inner tube has one or more holes into which vitreous tissue is drawn by suction and severed as the distal end of the inner tube is moved inward past the sharpened edge of the outer concentric tube, thereby implementing a pull-type cutting operation. Alternatively, the inner tube is sharpened at its distal end and the outer tube is provided with a sharpened distal opening to form a push-type cutter. In both embodiments, the inner tube is affixed directly to the piston and extends axially through to the opposite side thereof for connection to a flexible evacuation line which then passes out the back of the handpiece. The alternate air and suction pulses required for reciprocating the piston are supplied through a larger-diameter tube which coaxially receives the smaller evacuation line and also connects to the back of the handpiece. Although this manner of construction makes possible a fairly simple handpiece, interchangeability is sacrificed since the inner tube of the coaxial cutting assembly is affixed directly to the piston that reciprocates it. In addition, a potential problem of safety is presented by locating the connection point between the evacuation line and the inner tube within the compression zone behind the piston. If this connection were to fail for some reason, a direct path would be established between the pneumatic power supply and the interior of the eye by way of the inner tube, with possibly catastrophic results.
A similar pneumatic handpiece is disclosed in U.S. Pat. No. 3,884,238, also to O'Malley et al. As in the case of the previously-described handpiece, the inner reciprocating tube of the coaxial cutting assembly is affixed directly to the pneumatic piston and passes axially through a bore in the piston for connection to an evacuation tube on the opposite side thereof. In this case, however, the evacuation tube is a rigid metallic structure which slides through a bearing member at the back of the handpiece as the piston reciprocates. In addition, a metallic bellows is provided within the handpiece for containing the pneumatic compression and suction pulses required for reciprocating the piston. Isolation of the pneumatic power pulses from the inner tube of the cutting assembly still depends, however, on the integrity of the connection between the proximal end of the inner tube and the rigid evacuation tube on the pressurized side of the piston. Interchangeability of the coaxial tubular cutting assembly is again impeded, moreover, by the integral mechanical connection between the inner tube and the components of the reciprocating piston assembly.
A further known type of pneumatic handpiece for ophthalmic applications is described in U.S. Pat. No. 3,994,297, to Kopf. In this device, reciprocating motion for a coaxial tubular cutting assembly is provided by a piston which is displaced alternately in one direction by pulses of compressed air from a pneumatic source and in the other direction by a compressed return spring contained within the handpiece. The inner tube of the cutting assembly is rigidly connected to the forward portion of the piston and communicates with an axial bore formed therein. The axial bore communicates with an annular port, also formed in the forward section of the piston, which in turn slidably communicates with a vacuum passageway extending longitudinally along the inner periphery of the molded case of the handpiece and coupled to a vacuum line at the back of the handpiece. A pair of O-rings are provided to seal off the sliding connection between the annular port in the forward part of the piston and the vacuum passageway in the molded case of the handpiece from the remaining passageways and cavities of the handpiece. While this arrangement has the advantage of effectively isolating the vacuum connection to the inner tube of the cutting assembly from the pressurized zone behind the pneumatic piston, this is done at the expense of simplicity of construction, given the need for a rather elaborately bored and ported piston and the seals required for maintaining the sliding vacuum connection. In addition, the provision of a longitudinal vacuum passageway running parallel to the centrally located piston assembly necessitates an undesirable increase in the overall diameter of the handpiece. Finally, the rigid mechanical connection of the inner tube of the tubular cutting assembly to the reciprocating piston of the handpiece renders interchangeability of the cutting assembly impractical, if not impossible.